Wine 101: Passive Wine Cellars

Passive wine cellars use ground temperature to moderate the temperature swings and make the temperature swings seasonal instead of daily. Whereas refrigerated wine cellars can go anywhere in your house, a passive wine cellar must be located in a subterranean basement.

Annual Temperature Can Fluctuate

The graph above charts ground temperature variation over a year by depth below ground level. This chart is for a temperate climate and can vary if you go north to a colder climate or South to a warmer climate.

I picked two ground depths for discussion 7’-6” for an average basement ceiling height in an older home and 9’-6” for an average height in upscale newer homes. The funnel which looks like a champagne glass is the high and low temperature of the soil at a given depth. The closer you get to the surface the temperature of the soil swings broadly from summer to winter with an mean of 56 degrees. At 7’-6” which is represented by the first horizontal line the soil temperature varies from a low in the winter of 48 degrees and a high during the summer of 64 degrees with the mean of 56 degrees. At 9’-6” the temperature seasonal swing is 51 – 61 degrees. 55 to 56 degree is considered the ideal wine cellar temperature. Why, mostly because of convention. The European wine cellars of the famous wineries in Europe store their wines in deep caves, which are frequently stone quarries from Roman times. These caves are usually 20’ deep or more. At that depth they stay at the mean temperature of 56 degrees plus or minus less than one degree over the year.

A passive wine cellar in a home can never achieve the tight temperature range of the deep caves but it can make the swings moderate and seasonal. At 7’-6” the temperature swing is 16 degrees from 48 -64 and at 9’-6” the swing is 10 degrees 51-61. Without going into the why, which is the subject of another blog, the lower the temperature that wine is stored at the slower it ages. Temperature swings if significant, 14 degrees or more, cause your wine to breathe through the cork which increases the aging process significantly. If the temperature swing is seasonal the damage is much less then if it is daily by a factor of 365 days.

To create a passive cellar in your home basement, you allow the cool temperature from the floor to enter while you block out the higher temperature from the house and higher ground levels on the exterior walls. The diagram above shows a passive wine cellar construction detail. By using a vapor barrier and high R value insulation, you block temperature exterior to the wine cellar and allow the ground temperature from the floor to enter. In this case the exterior concrete basement wall was insulated on the outside but it can also be insulated from the inside. To this you need to add an exterior grade door with full 360 degree weather seal around it.

Higher temperatures and significant temperature swings accelerate the aging process which is not necessarily a bad thing if done on a controlled basis like a passive cellar. It just means your wines are ready to drink earlier. Where this does make a difference is maintaining your wine in the optimal drinking range once they have peaked. Many whites and some reds are at their peak when bottled. Some reds take years to age to their peak. Once at their peak you want to keep them there to enjoy as long as possible. The proper cellar environment is the key. A refrigerated cellar gives you total control but a passive cellar is the next best thing.

Contact us to speak with one of our expert Design Specialists to figure out how you can let your wines properly age.

So, if I have a basement wine room which is actually bumped out from the main wall so that three of the sides of the wine cellar are exterior poured concrete walls, can I just insulate and barrier the ceiling? The fourth side of the “box” will be frameless glass and there will not be any vent in the wine cellar.

SSP
You have a great situation for a passive cellar. As you said, you need insulation and vapor barrier on the wall that is not below grade and ceiling. In addition you will improve your passive cellar condition by insulating 30-36″ below grade on the other three walls. That is frost line in the temperate zones and the ground above that point will fluctuate during the seasons. In addition you want to put a vapor barrier down to the floor on those three exterior walls. You can get moisture that penetrates through the concrete even if you don’t see water. For the same reason is would be wise to seal the concrete floor with a good paint or concrete sealer with tile or other covering on top.

Thank you for the information. I wonder if by using a vapor barrier even on the three exterior walls it might end up with lower than ideal humidity? The rest of the basement is being finished and will be climate controlled although the temperature is generally so pleasant that neither heat nor AC will be used very often. The back part of the basement where the cellar will be located also does not have any windows. We are going to seal the concrete and use a decorative stain. What is the insulation of choice. I will definitely have them insulate down a few feet from the top. Although, even there, the exterior is a patio (which is why there is no window cut out) which has a cement slab then dry laid limestone so it takes a lot to get through to the poured walls. The house was built in 2009 so I’m sure that the exterior walls have some sort of coating on them (as I recall it looks like black tar?) that must be the water barrier. Thanks again for the help.

SSP
Those exterior walls would not have to be sealed on the inside if they are sealed on the outside. If you have a good vapor barrier on the interior wall and ceiling and the door has a good gasket seal, then the cellar is going retain any humidity that comes from the outside walls or floor if they are unsealed. Being a new home and treated the way you describe that probably is not a concern. High humidity is a good thing as long as it doesn’t go past a point. I keep my wine cellar at 75% relative humidity. 80% or higher can start to create mold and mildew conditions. The higher humidity keeps the corks swollen and keep the wine from wanting to wick out over time.